全文获取类型
收费全文 | 124614篇 |
免费 | 1859篇 |
国内免费 | 237篇 |
专业分类
教育 | 86580篇 |
科学研究 | 13446篇 |
各国文化 | 1979篇 |
体育 | 9774篇 |
综合类 | 172篇 |
文化理论 | 1080篇 |
信息传播 | 13679篇 |
出版年
2021年 | 950篇 |
2020年 | 1659篇 |
2019年 | 2560篇 |
2018年 | 3129篇 |
2017年 | 3355篇 |
2016年 | 3409篇 |
2015年 | 2305篇 |
2014年 | 3173篇 |
2013年 | 27236篇 |
2012年 | 2398篇 |
2011年 | 2776篇 |
2010年 | 2333篇 |
2009年 | 2612篇 |
2008年 | 2424篇 |
2007年 | 2151篇 |
2006年 | 2406篇 |
2005年 | 2375篇 |
2004年 | 3069篇 |
2003年 | 2342篇 |
2002年 | 2185篇 |
2001年 | 2126篇 |
2000年 | 1792篇 |
1999年 | 1660篇 |
1998年 | 1472篇 |
1997年 | 1532篇 |
1996年 | 1698篇 |
1995年 | 1467篇 |
1994年 | 1478篇 |
1993年 | 1472篇 |
1992年 | 1576篇 |
1991年 | 1483篇 |
1990年 | 1464篇 |
1989年 | 1398篇 |
1988年 | 1259篇 |
1987年 | 1194篇 |
1986年 | 1214篇 |
1985年 | 1485篇 |
1984年 | 1327篇 |
1983年 | 1328篇 |
1982年 | 1270篇 |
1981年 | 1197篇 |
1980年 | 1186篇 |
1979年 | 1311篇 |
1978年 | 1229篇 |
1977年 | 1138篇 |
1976年 | 1029篇 |
1975年 | 833篇 |
1974年 | 832篇 |
1973年 | 804篇 |
1971年 | 666篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
Walter Hahn Guy Cellerier Wolfgang Wilhelm Jindra Kulich Robert J. Havighurst Bryan T. Peck Annegret Körner Rodney Skager Renate Nestvogel J. H. Sislian John J. Bergen Peter W. Kahl Tony Bates 《International Review of Education/Internationale Zeitschrift für Erziehungswissenschaft/Revue internationale l'éducation》1978,24(4):523-544
933.
934.
P. Hammond 《Journal of The Franklin Institute》1978,306(2):133-157
Electromagnetic fields can be treated as systems in which the field equations are the equations of equilibrium. This formulation draws the subject into the unified approach of mechanics. Close analogies to potential and kinetic energy exist and these can be used to provide double bounds to the electromagnetic energy. 相似文献
935.
A new active R filter which realizes a second order bandpass transfer function is given. The network employs only resistors and two operational amplifiers. Sensitivities to all passive and active circuit components are very low. Design equations are given and experimental results are also included. 相似文献
936.
937.
This paper introduces a polynomial operator called the DT-polynomial as a novel approach to network flow problems. The class of networks dealt with is time-varying in the sense that the capacity, cost, and travel-time of each edge may vary in discrete time. The Dt-polynomial is a polynomial in two operators, D (delay) and T (time), which is used for describing the time-varying transmission characteristics. The paper starts with the mathematics involving the DT-polynomials. A new shortest arrival route algorithm is presented, and its computational complexity is found to be favorable in comparison with others such as Dijkstra's method and the potential method derived from Ford-Fulkerson's technique. Furthermore, a dynamic flow problem is formulated and analyzed in terms of DT-polynomials, and a latest-departure earliest-arrival schedule is given. Finally, a modified DT-polynomial is applied to digital filter networks. 相似文献
938.
M. Farshad 《Journal of The Franklin Institute》1978,305(3):125-135
A two-dimensional theory for the incremental deformations of an initially stressed continuum with couple stresses is established in this paper. As applications of theory, the problems of internal instability and wave propagation are studied. It is found that the otherwise non-dispersive waves become dispersive, and additional local modes of buckling and vibratory motion are observed. To complete the theory, a stress function formulation of equations is also presented. 相似文献
939.
Yudell L. Luke 《Journal of The Franklin Institute》1978,305(5):259-273
Uniform asymptotic estimates for the error in the main diagonal and first two subdiagonal Padé approximants for exp(iz) in a sector covering the real z axis are derived. The results are applied to analyze the error in a cerain procedure for the numerical inversion of the Laplace transform. 相似文献
940.
In an attempt to clarify the chronological relationship between identity and equivalence conservation, normal preschool-aged children (experiment 1) were exposed to brief videotape demonstrations of a model conserving identity and equivalence, identity only, equivalence only, or neither. Subsequent performances indicate that identity was easier to accelerate than equivalence, and training in both identity and equivalence appeared to be most effective in accelerating conservation. Trainable mentally retarded (TMR) children were then exposed to either the identity-equivalence-conserving or control model (experiment 2). This population, which some have argued remains at a preoperational level of functioning, was more likely to conserve identity than equivalence. In addition, conservation in the training group increased following training, though these gains were not maintained over a 3-week retention interval. 相似文献